The present invention relates to a measuring apparatus and method of making it, particularly for measuring a diameter of a hole or distance between surfaces and a method of making the apparatus. The present invention has particular applicablity to measuring of small bores by insertion of a gage portion therein.
Measurement apparatus for measuring distance between two surfaces (or the diameter of a bore or hole) have been known for some time. In such systems, it is desirable to measure accurately the distance between two closely-position surfaces. A mechanical apparatus including the elements necessary for a mechanical measurement must be small to be inserted into such a small area. In view of the small access area, it is frequently necessary to measure these dimensions indirectly as by movable gaging tips which engage the surfaces and a movable tapering stylus to measure the separation between the tips by the contact tips. Such a stylus makes a frictional engagement with the contact tips which provide inaccuracies and do not lend themselves to highly repeatable measurements. Additionally, the stylus must be accurately manufactured, and may wear during use, leading to inaccuracies in measurements.
Such systems also lack, in some instances, an interchangeable spindle, requiring that the entire gaging assembly (spindle and measuring elements) be provided for each range of dimensions. In measurement systems, it is desirable to have a probe assembly which a portion is common fitted with interchangeable spindles which can measure various diameter holes with accuracy. For example, a particular spindle may measure the diameter of holes between 20 and 25 millimeters. To measure a hole of approximately 30 millimeters, a different spindle will be required and advantageously would fit onto a common measuring element. It is advantageous that merely the front spindle be changed and the rear measuring elements, including gaging cartridge, handle assembly and coupling to a readout system, not be changed for each change in dimension to be measured.
Some examples of prior art devices which are suited for such measurement are shown in U.S. Pat. Nos. 2,665,496; 2,239,981; and 2,781,585.
Of course, it has been suggested in the prior art to provide an air gaging apparatus for measuring diameters of holes and other distances between surfaces. Such gages work reasonably well to an inherent accuracy, but it is time-consuming and expensive to make an accurate air gage and requires costly know-how to set up. Further, air gages require a source of air under constant pressure and other miscellaneous devices such as pressure regulators and filters which may not be available in many manufacturing environments. Accordingly, such air gage apparatus have undesirable limitations and disadvantages for some measuring applications. Example of such air gaging spindles and/or systems are shown in U.S. Pat. Nos. 2,926,523; 2,755,558; 2,995,921; 2,914,860; 2,889,704; and others.
Accordingly, the foregoing prior art gaging apparatus has significant limitations and disadvantages.